Experimental study on acoustic streaming in water containing microcapsules

Microbubbles strongly affect the sound field in a medium and various phenomena are caused by this sound field. In particular, in this study, the influence of microbubbles on acoustic streaming in water is quantitatively investigated by an experimental method. In order to ensure a constant distribution of microbubbles in water with time, and to appreciate the quantity of the microbubbles, water containing a certain amount of microcapsules packed in a cell is prepared. The streaming velocities are measured using a laser Doppler velocimeter (LDV). The observed results evidently show that the acoustic streaming velocity in water increases due to the microcapsules, and fluid-dynamic nonlinearity affects both velocities with and without microcapsules at a high sound pressure. This nonlinearity controls the velocity with microcapsules at a low sound pressure and also causes the dependence of the ratio between the streaming velocities of the medium with microcapsules and that without microcapsules on the sound pressure.